Method and apparatus for selecting and prescribing audiphones



PERCENTAGE HE ARING' March 29, 1938. 5 LYBARGER 2,112,569

METHOD AND APPARATUS FOR SELECTING AND PRESCRIBING AUDIPHONE S FiledJune 16, 1936 4 Sheets-Sheet l F/al. .F/6.4. I

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PERCENTAGE HEARING L035 3 3 g E '8 g 8 3 FREQUENCY FREQUENCY WIT/VFJJI'SINVENTOR.

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March 29, 1938. 5 LYBARGER v 2,112,569

METHOD AND APPARATUS FOR 'SELECTING AND PRESCRIBING AUDIPHONES FiledJune 16, 1936 4 Sheets-Sheet 2 IG-7 T Fici.

RESPONSE RES PONJE FREQUENCY FREQUENCY 40% nuzosm INVENTOR.

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March 29, 1 38- s. F. LYBARGER METHOD AND APPARATUS FOR SELECTING ANDPRESCRIBING AUDIPHONES 4 Sheets-Sheet 3 Filed June 16, 1936 VENTOR. i Xif; ATTORNEYS.

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March 29, 1938. $3 LYBARGER v 2,112,569

METHOD AND APPARATUS FOR SELECTING AND PRESCRIBING AUDIPHONES Filed June16, 1936 4 Sheets-Sheet 4 I B" I J 104 103 J VENTS: I M 22M WIN/5555 BY6 M W MWV '4 ATTORNEYS.

Patented Mar. 29, 1938 UNITED STATES 'PATENT' OFFICE BEETHOD ANDAPPARATUS FOR SELECT'HVG AND PRESCRIBING AUDIPHONES Lybarger ApplicationJune 16, 1936, Serial No. 85,502

8 Claims.

This invention relates to a method and apparatus for determining andprescribing the proper hearing aids for people whose hearing isdefective.

In the past it has been the customary practice for manufacturers ofhearing aid equipment to furnish for all purposes audiphones, or hearingaids as they are commonly referred to, of more or less standard orsubstantially fixed characteristics. Although such practice has met witha 10 measure of success, it is far from satisfactory and leaves much tobe desired. Hearing aids as furnished seldom, if ever, fit the userproperly because, among other reasons practically every case of hearingloss is different. For example, one persons impairment may be largelyover the higher frequency ranges while another is over the lowerfrequency ranges, and in substantially all cases they vary widely overthe complete hearing ranges, Consequently, while a standard aid may bedesigned to satisfy as near as possible the average case of hearingimpairment, the result is that it actually does not satisfy anyproperly; and this is true of both the air and bone conduction aids.

It may seem to those unacquainted with the facts that if hearing aidsamplified all sounds the same amount, the amplification could be ,madeso as to bring the hearing of the afllicted person up to the normallevel and everything would be satisfactory. But this is not the case noris it possible or desirable. In the first place,

no present day portable hearing aid amplifies all sound frequencies thesame amount. In the sec 0nd place, people with impaired hearing becomeaccustomed to a certain amount of distortion with some sounds softerthan others even though actually all of those sounds may have the samephysical intensity. Consequently, if it is attempted to bring all suchsounds up to the same level of amplification the distortion pattern mustbe changed. This makes it necessary for the patient to cultivate newhearing habits, and the strain thus placed on him by this and by thedistortion of the distortion pattern he had become accustomed to areoften irritating and nerve-wracking. To avoid this, it is highlydesirable that hearing aids be individually fitted and prescribed sothat each individual case will receive the hearing aid most suitable forit, that is an aid which affords a user the clearest possible receptionwith a minimum of nervous irritation.

This invention provides for the use of an accurately calibrated masterhearing aid which is capable of being varied over wide ranges to providea large number of different amplification characteristics. As willpresently appear the am- 1 plification characteristics are variable in alogically arranged fashion, so that gradually controlled characteristicsin any principal portion of the audible sound spectrum are available.This makes it possible to reproduce for comparison or test, almost anydesired amplification characteristic and enables the most satisfactoryampli fication characteristic by either air or bone conduction to befound for a given hard of hearing person. As a further feature itprovides for readily-determining the degree of amplification, as well asthe shape of the amplification curve. With these factors known, ahearing aid may be produced by any desired means, or by any suitablyequipped organization or person, which will satisfy their requirementsas determined by the apparatus of this invention.

To attain such end in accordance with this invention, advantage is takenof the fact that the overall characteristics of a hearing aid aredetermined by the integrated response characteristics of its componentparts. These comprise essentially the microphone, the ear-phone, and theamplifier, although in some cases the latter may not be needed. Withinlimits, it has been found that the response characteristics of thesedifferent elements can be readily and controllably varied and that byvarying them a variation in the amplification of the aid in differentfrequency bands can be obtained within a reasonable degree ofindependence. Consequently, by providing a plurality of these unitshaving various characteristics to select from and properly combiningthem, an amplification characteristic may be provided which will satisfymost any requirement.

To make it possible. for a person needing a hearing aid to actuallyselect by tests the characteristics necessary in an aid to suit it tohis own requirements, an apparatus is provided which is equipped with aplurality .of both bone and air conduction ear-phones or receivers, aplurality of microphones, and a plurality of amplifiers, all havingdifierent response characteristics. To readily connect these elementstogether for test purposes, they are suitably con nected to switcheswhich are adapted to quickly connect any one of the elements in anygroup to any one 'of the elements in each of the other groups so that atest hearing aid may be chosen having any desired combination of theresponse characteristics of the elements provided in the testingapparatus. The total number of different response characteristics orcombinations available is, of course, equal to the product of the numberof the microphones, the number of amplifiers, and the number of thereceivers provided, plus the product of the number of microphones andreceivers. To secure a wide range of difierent overall amplificationcharacteristics, the response characteristics of each group of theseelements are preferably designed to cover a considerable range of tonefrequencies.

To facilitate the testing of each group of elements or certain portionsthereof they are preferably provided with graduated characteristics soas to make it possible to control the amplification in a given frequencyregion without appreciably affecting the other portions of the frequencyspectrum.

For example, the microphones may be designed to produce the principalchanges of amplification characteristics in the frequency regions below800 cycles per second, the head phones or receivers to produce theprincipal changes of amplification characteristics in the frequencyranges of from 800 to 1500 cycles per second, and the amplifiers toproduce the principal changes of amplification characteristics in thefrequency ranges from 1500 to 4000 cycles per second. This may, ofcourse, be otherwise accomplished, as, for example, by modifying thedesign of the different elements to influence different frequencyregions, and such' is contemplated by the invention.

When the most satisfactory selection of microphone, receiver andamplifier combination has been made, the operating characteristics ofsuch elements being known, the overall operating characteristics of theselected combination are determined. With this knowledge an audiphonecan be readily provided by the manufacturer using any combination ofelements which provide the desired characteristics or one can beassembled by including in it elements having the same responsecharacteristics as the element selected by the'afflicted person. Amongthe advantages, it makes it possible for the manufacturer toconveniently and economically provide audiphones identical orsubstantially identical with the audiphone which a customer has selectedas fitting his own particular requirements. In addition, such a. methodof providing aids not only makes for better results but to a very greatextent saves the customer the annoyance of having to use an audiphonewhich distorts his reception of certain sounds to such an extentas to beirritating, which in the past has been one of the chief sources ofcriticism of a good share of the audiphones used.

In order to further improve the efliciency of the testing apparatus andalso make it possible for the user to select an aid which will give thebest satisfaction under normal conditions of usage, it is preferablyprovided with means for varying the voltage supply for the aid. Withsuch means, a more sensitive test can be run on the elements beingselected and an aid can be more accurately selected which will functionproperly over a greater period of the life of the batteries used in it.In other words, it is desirable to select an aid which will functionsatisfactorily when a battery is below its maximum charge in order thatthe aid will give the greatest amount of satisfactory service for thelife of the battery. With the minimum voltage at which the instrumentscan be satisfactorily used known the life of a given type of a batterycan be predicted with reasonable accuracy.

,sents the hearing ability at all frequencies.

With the foregoing in mind it is an object of this invention to providea method and apparatus for selecting the most satisfactory amplificationcharacteristics to meet individual requirements.

A more specific object is to make available at a 'minimum cost a widerange of different response characteristics from which an individual mayaccurately select one which will most effectively satisfy his ownrequirements. Another object is to make possible for a person to notonly have a wide range of characteristics to choose from but to make itpossible for him to effectively compare his. reaction to differentcharacteristics when making his selection, and also compare his reactionto bone and air conduction receivers.

A further object is to provide in a testing apparatus of the characterreferred to for varying the value of the voltage supplied to the aid soas to give it a larger degree of testing sensitivity and also make itpossible to select an aid which will give the greatest satisfaction overthe life of the batteries employed in it.

It is also an object to provide a testing apparatus which is adapted topermit a patient to compare different amplification characteristics witha minimum lapse of time between tests, which is highly desirable becauseof the inability of a person to accurately recollect his reactions todifferent tests where they are separated by more than extremely shortintervals. These and various other objects as well as the various othernovel features of the invention will be apparent when the followingdetailed description is read in conjunction with the accompanyingdrawings of which Fig. 1 is an audiogram of person with perfect hearing;Figs. 2 and 3 audiograms of two different people afflicted withdefective hearing; Fig. 4 responsive curves of three differentlydesigned microphones; Figs. 5 and 6 similar curves of three differentlydesigned ear-phones and amplifiers respectively; Figs. 7 and 8 diagramsshowing the individual response curves of the microphones, ear-phonesand amplifiers employed in two different audiphones together with theresultant response curves of the audiphones themselves;

Fig. 9 an elevational view of a testing apparatus constructed inaccordance with the invention; Fig. 10 a view looking into the top ofthe cabinet shown in Fig. 9 with the cover removed; Fig. 11 a circuitdiagram for the apparatus shown in Fig. 9; Figs. 12 and 13 a plan andsectional view respectively of an adapter for interchangeably using' aplurality of ear-phones with a single ear tip; Figs. 14 and 15 viewssimilar to Figs. 12 and 13 of a modified form of ear-phone adapter;Figs. 16 and 17 a view also similar to Figs. 12 and 13 of still anotherform of earphone adapter; Fig. 18 a schematic view of a system ofapparatus for determining what amplification characteristics best suit apatients hearing loss.

As shown by the audiogram in Fig. 1, wherein the horizontal axis is.plotted in terms of frequency or pitch and the vertical axis is plottedin terms of hearing ability, the perfect ear responds uniformly to allaudible frequencies as indicated by the straight line a which repreanimpaired ear heard all sounds like the perfect ear except for a uniformloss in intensity, the line of hearing would still be a straight linebut below the line obtained from a perfect ear.

This condition, however, rarely ever exists in reality. As inpractically all cases of impaired hearing, as previously stated, thereis practically never a uniform loss of hearing over all pitches. Asillustrated in Figs. 2 and 3, which show the audiograms of two actualcases of defective hearing, the loss of hearing varies quite widely overdifferent frequencies, as, for example, in the case shown in Fig. 2, thehearing loss is high in the low frequencies and low in the highfrequencies, which in the case shown in Fig. 3 is practically reversedin these zones.

Theoretically, it would seem that the proper hearing aid for anindividual having defective hearing would be one having amplifyingcharacteristics which are just the opposite of the users loss of hearingas indicated by his or her audiogram, that is, one which wouldjust bringthe hearing reception up to normal at all frequencies. In practice,however, this is seldom the case because among other reasons due to thewide variations in loss of hearing at different frequencies and the longperiod over which a user has become accustomed to such form of hearing,they find that if it is attempted to give them normal hearing over allfrequencies the extreme amplification required over the most affectedzones is irritating and confusing as well as tiring. Hence if it isattempted to provide such a hearing aid it is usually found to.beunsatisfactory for the reasons mentioned.

The properly constructed hearing aid is one which approaches thedefective persons amplification requirements as indicated by hisaudiogram, but which does not produce anervous reaction or is tiring tothe user. As stated hereinbefore, the amplification characteristics ofan audiphone are determined by the integrated response characteristicsof the microphone, earphone, and amplifier going to make up theaudiphone. In practicing the present invention a variety of theseelements having graduated varying characteristics is provided and theseselectively assembled under the guidance of the patients in such a waythat the patient is most effectively fitted as determined by his or herrequirements.

In fact by properly designing these elements they can be adapted toquite effectively regulate the overall response characteristics ofaudiphones in only certain frequency bands without greatly modifying theresponse in the other sound regions. For example, as shown in Fig. 4,wherein the curves A, B, and C designate the response characteristics ofthree different micro phones, the microphones may be designed to varythe response characteristics ofv an audiphone for tones up to 800cycles. Likewise, as shown in Fig. 5, wherein the curves M, N, and Odesignate the response characteristics of three different ear-phones,the ear-phones may be designed to vary the response characteristics ofthe audiphones for tones from 800 to 1500 cycles. Similarly, as shown inFig. 6, wherein the curves X, Y, and Z designate the response curves ofthree different amplifiers, the amplifiers may be designed to vary theresponse characteristics of an audiphone for tones ranging from 1500 to3000 or 4000. To secure the widest possible range of amplificationcharacteristics the response characteristics of the elements in eachgroup are preferably made to cover as broad a range of frequencies as ispossible within the particular frequency zone which they primarilyaflect.

The possibilities of a collection of elements such as designated inFigs. 4, 5, and 6 will be appreciated when reference is had to Figs. 7and- 8. In Fig. '7 the curve D shows the amplification characteristicsof an audiphone which is made up of a microphone having a response curveC,

an ear-phone having a response curve N, and an amplifier having aresponse curve Z. In Fig. 8 the curve E shows the amplificationcharacteristics of an audiphone made up of a microphone having aresponse curve A, an ear-phone having a response curve N, and anamplifier having .a response curve Y. With the provision of threedifferent instruments in each group, the response curves for which arepreferably furnished, 36 different combinations can, of course, be madeup, 27 using the amplifiersand 9 without, and obviously this may beincreased or varied by varying the number of instruments in each group.As will be also obvious, a persons audiogram will aid in selecting theproper combination of such elements to satisfy his particular hearingloss because those to be tried out can be limited to the ones which theoperator Will know correspond most closely with the audiogram. However,through the use of the apparatus to be presently described it isunnecessary to have an audiogram in order to make the proper selections.

Referring to Fig. -9 of the drawings, suitable apparatus for carryingout this invention is shown as comprising a portable cabinet I having afront panel 2 on which are mounted a main switch 3, rheostat 4,voltmeter 6, three instrument switches l, 8, and 9, a set of microphoneterminals II, a set of earphone terminals l2, and pilot lamps I3adjacent the terminals for indicating which terminals are' in use. Tothe microphone terminals are connected a plurality of microphones l4,and to the remaining terminals a. plurality of air conduction and boneconduction ear-phones, I5 and l5a, respectively, are connected.

Disposed inside of the cabinet, as shown in Fig. 10, are a plurality ofamplifiers l6, batteries H for the audiphones, a battery l8 for thepilot lamps, and the necessary wiring for interconnecting the variouselements of the apparatus. The wiring diagram for the apparatus is shownin Fig. 11 and will now be described.

The microphone-selector switch I is a multiple contact type of gangswitch equipped with a series of spaced sliding contact arms la, lb, 1c,1d, le, and if which are insulated from the common actuating shaft 1gand are disposed to engage a co-operating series of' spaced contacts 2I, 22, 23, 2t, 25, and 26, respectively, or contacts 21a, 22a, 23a, 24a,25a, and 2611, or Zlb, 22b, 23b, 25b, 25b, and 26b. The first series ofcontacts, except contact 26, are connected by wires 21 to one of themicrophones, and the second and third series of contacts are likewiseconnected, respectively, to the other two microphones, except thatcontacts 25, 26a, and 2617 are each connected to a. pilot lamp I3.Switch arms la, 11), and Te are connected by wires 28a, 28b, and 280 toswitch arms 8a, 8b, and 80, respectively, of the amplifier selectorswitch 8 which is also of the gang type. Switch arms 1d and 1e areconnected by wires 29 to switch arms 9a and 91), respectively, of theear-phone selector switch 9.

The arms of the amplifier switch are disposed for engaging any one offour series of contacts 3|, 32 and 33; Ma, 32a, and 33a; 3"), 32b, and33b; or 3lc and 330. Contacts 3|, 32 and 33 are connected by wires 36a,36b and 360 to one of the amplifiers l6, contacts 3|a, 32a, and 330. areconnected by wires 31a, 31b and 310 to another of the amplifiers, andcontacts 3"), 32b, and 332) are connected by wires 38a, 38b, and 38c tothe remaining amplifiers. Contacts 3lc and 330 are connected by wires 39and ll, respectively to batteries l1, and battery wires 39 and 4| areconnected by wires 42 to the battery terminals of the amplifiers.voltmeter 8 is shunted across the battery wires, and rheostat 4 and mainswitch 3 are connected in series in wire 39. Shunted across thebatteries between the rheostat and wire 39 is a condenser 43 which isemployed to reduce the effective internal impedance of the supplycircuit to a value not exceeding appreciably the internal impedancegenerally found in a battery, which has the result of preventingcombinations of instruments.

oscillation or degeneration in the hearing aid circuit which, ifpermitted, causes serious distortion in the quality of the transmittedsounds.

The ear-phone switch arms 9a and 9b are disposed for engaging any one ofthree groups of contacts 44 and 45; a and 450. or b and 45b that areconnected by wires 41 to the three bone conduction receivers l5a. Theswitch arms are also adapted to engage any one of three groups ofcontacts 5| and 52; 51av and 520., or 5") and 52b, that are connected bywires 54 to the three air conduction receivers l5. The ear-phone switchis also provided with an arm 90 that is adapted to engage a series ofcontacts 56 connected to one side of six pilot lamps l3 that indicatewhich ear-phone is in circuit. The other side of the lamp is connectedby a wire 51 to one side of battery l8 the opposite.

terminal of which is connected through switch 3 and wire 58 to switcharm 80. Wire 58 is also connected by wire 59 to arm I! of the microphoneselector switch, while wire 51 is connected by a wire 6| to themicrophone pilot lamps, whereby the latter likewise receive electriccurrent from battery I8.

It will be understood that each of the various microphones, amplifiersand ear-phones used in this apparatus has characteristics known to bedifferent from those of the others. ly, a large number of combinationsof these characteristics can be obtained by merely operating the threeinstrument switches to select different The number of combinations canbe increased by making the cabinet large enough to accommodate moreinstruments. On the other hand, if desired, the amplifiers can be cutout of the circuit by turning the amplifier switch 8 until contacts 3lcand 330 are engaged. This permits the current from batteries I! to flowthrough the microphones and receivers without passing through theamplifiers.

In using this apparatus to find the most satisfactory amplificationcharacteristics for any given individual, the various combinations ofinstruments made possible by the selector switches may be tested underthe same normal conditions by attaching a microphone to the clothing ofthe person with defective hearing, and connecting an ear-phone to thisear. with each combination he is asked to state his reaction to the testsounds, such as their loudness, clarity, pitch, and freedom from nervousirritation. His reaction will, of course, indicate that certaincombinations may be eliminated and reduce the tests required. Thetesting may also be expedited somewhat if an audiogram of the patientshearing is available, as it will to a certain extent function as a guidefor ceivers l5.

Consequentdetermining the possible combination which will satisfy thepatient. After the most suitable combinations have been determined, thetests can be repeated on these to find the one most satisfactory fromall standpoints.

Within the audible sound frequency range the ear-phones in thisparticular embodiment are designed to be most responsive to variation inthe lower zone, the microphones in the middle zone, and the amplifiersin the upper zone. Consequently, amplification in the lower zone isvaried primarily by the microphones, in the upper zone it is controlledby the amplifiers, and in the middle zone by the ear-phones. By knowingthese facts, an operator can approximately select the instrument thatwill give the desired amplification in the desired zone. For example, ifa particular test combination enables the patient to hear well allsounds except those of low pitch, the operator will switch in anothermicrophone having higher response characteristics because he knows thatamplification in the lower frequency zone is controlled by themicrophone.

An important feature of this apparatus is that the change from onecombination to another can be made so quickly that the patient canaccurately compare the results with those of the one just preceding andjust succeeding. As far as a change of microphones or amplifiers isconcerned this quick change is made by merely turning the microphone andamplifier switches, but with the air conduction ear-phones it isnecessary to connect a new one to the patients ear every time a changeis desired. To permit a quick change of air conduction ear-phones theadapter shown in Figs. 12 and 13 may be provided. This device consistsof a block ll provided with passages 12 extending inwardly from itssides to a point from which a passage 13 extends outwardly at rightangles to passages 12. The number of passages 12 depends upon the numberof receivers that are to be attached to the block, the drawings showingfour passages and four re- The tip |5b of each receiver is mounted in asocket 14 at the outer end of the passage communicating with thereceiver. An ear tip 16 that would ordinarily be connected to a receiveris connected to a tip 11 projecting from the block at the outer end ofpassage 13. Thus, all the air conduction receivers are in communicationwith the ear tip at all times; however, only.one-receiver is operated ata time. With this device is is possible to instantly switch from onereceiver to the other without removing the ear tip from the ear.

In Figs. 14 and 15 there is shown a modification which has the advantagethat only one receiver is in communication with the ear tip at a time,and there is therefore a much smaller column of air in the block 8|, andit is impossible for the other receivers to absorb some of the soundcoming from the receiver in use. In this embodiment the block 8| isprovided with a central bore 82 extending part way through it with whichthe various passages 83 connect. Rotatably secured in this bore by aplate 84 is a plug valve 85 the outer end of which is knurled to providea knob 81 for turning it. The inner end of the plug is provided with anarcuate passage 88 which is adapted to connect the passage leading tothe ear tip with any one of the passages leading to the receivers.Consequently, only one receiver at a time can be connected with the eartip, but it is possible to quickly switch from one receiver to anotherby turning the plug. 'To hold the arcuate plug passage in registry withany desired receiver passage the plug is preferably provided around itsperiphery with shallow recesses 89 into which a ball 90 is pressed by aspring 9| disposed in a bore 92 in the block. The recesses are sopositioned that when the ball engages them one of the receiver passages83 is in communication with a plug passage. p

The modification shown in Figs. 16 and 17 is the same as that justdescribed except that instead of being turned manually by a knob, theplug 93 is turned electrically. The outer end of the plug is providedwith a shaft 94 to which a permanent bar magnet 95 is rigidly connected.Disposed between block 96 and the magnet is a soft iron core 91 in theform of a cross having outwardly turned ends spaced from the magnet.Each arm of the core is encircled by a coil 98 each of which isconnected through a switch (not shown) to a battery. The coils are soWound that When an electric current is passed through any one of themthe polarity of the adjoining portion of the core is made such that itattracts one endof the permanent magnet. By connecting the coils to thecontacts of the air conduction receiver switch the magnet can be made toautomatically turn to the proper position for connecting the desiredreceiver with the ear tip when the earphone selector switch connectsthat receiver into the hearing aid circuit.

The effectiveness of this apparatus depends to a considerable extentupon the accuracy of testing the ability of the patient to hear with thevarious test combinations. In Fig. 18 there are shown several differentdevices for conducting an accurate test of the efiiciency of each testcombination of instruments. The patient llll is seated beside thetesting apparatus described herein, and the desired microphone andear-phone are connected to him. Spaced a suitable distance in front ofhim is a reproducing system consisting of a phonograph turn-table andpick-up I02, volume control I03, amplifier I08, a meter N16 forindicating the electrical output of the amplifier, and a reproducer orloud speaker I07. A record, on which has been recorded a list ofsentences, words, numbers or syllables, is placed on the phonograph andas it is played the patient is required to either write down or stateWhat he hears. In this way the intensity of the sound produced for thepatient remains uniform as various combinations of instruments aretested by him.

The phonograph record may be supplemented by a michophone Ill into whichthe operator makes whatever sounds he pleases. The amplifier meter I06is used to keep the intensity of the sounds coming from the reproducerat a reasonably constant value. The volume control Hi3 may be used toreduce or increase the intensity of the sounds.

Another way of testing the hearing of the patient which can supplementthe method just described, or be used in place of it if desired, is tohave the operator H2 speak directly to the patient. However, as it isvery difiicult for a person to maintain his voice at a constant levelover any considerable period-of time, which is necessary in order tomake an accurate test, a

microphone H3 is placed beside the patient and is connected by anamplifier H4 to a meter H5. The speaker can watch the meter I I5 as hetalks and thereby maintain his voice at substantially the same levelthroughout the test.

Among the chief advantages of this invention,

as will be appreciated from the foregoing, is the fact that it enablesone to determine the most suitable amplification characteristic directlywithout the necessity of judging or guessing the supposedly propercharacteristic from an audiogram, if the audiogram only is available.

Another advantage not previously mentioned is that it provides means forreadily determining from time to time as a persons hearing requirementschange what modifications are needed in the amplificationcharacteristics he needs to give him continued satisfactory hearingreception.

According to the provisions of the patent statutes, I have explained theprinciple and mode of practicing my invention and have illustrated anddescribed what I now consider to represent its best embodiment. However,I desire to have it understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallyillustrated and described.

I claim:-

1. The method of selecting the most suitable audiphone for ahard-of-hearing person, comprising providing a plurality of at least twoof the different types of instruments forming an audiphone, the severalinstruments of each group of like instruments having preselecteddifferent response characteristics in a predetermined portion of thefrequency range transmitted by the audiphone, said portion beingsubstantially different from the portion of said frequency range inwhich any other group of the audiphone-forming instruments haspreselected diflerent response characteristics, establishing auditorycommunication between said person and any desired combination of unlikeinstruments,.and forming the combinations by successively combining eachof the instruments in one group with one of each of the other types ofaudiphone-forming instruments to find the instrument having the mostsuitable response characteristics in a portion of said frequency rangeand then repeating this procedure with another group to find theinstrument having the most suitable response characteristics in anotherportion of the frequency range.-

2. The method of selecting the most suitable audiphone for ahard-of-hearing person, comprising providing a group of microphoneinstruments having preselected different response characteristics in apredetermined portion of the frequency range transmitted by theaudiphone and a group of ear-phone instruments having preselecteddifferent response characteristics in another portion of said frequencyrange, establishing auditory communication between said person and anydesired combination of microphones and receivers, and forming thecombinations by successively combining each of the instruments in onegroup with one of the instruments of the other group to find theinstrument having the most suitable response characteristics in aportion of said frequency range and then successively combining each ofthe instruments of the second group with said most suitable instrumentof the first group to find the instrument having the most suitableresponse characteristics in another portion of said frequency range.

3. The method of selecting the most suitable audiphone for ahard-of-hearing person, comprising providing a group of microphoneinstruments having preselected different response characteristics in apredetermined portion of the frequency range transmitted by theaudiphone and a group of ear-phone instruments having preselecteddifferent response characteristics in another portion of said frequencyrange and a group of amplifier instruments having preselected difierentresponse characteristics in the remaining portion of said frequencyrange, establishing auditory communication between said person and anydesired combination of three unlike instruments, and forming thecombinations by successively combining each of the instruments in'onegroup with one instrument of each of the other two groups to find theinstrument having the most suitable response characteristics in aportion of said frequency range and then repeating this procedure witheach other group to find the instruments having the most suitableresponse characteristics in the other portions of the frequency range.

4. 'I'hemethod of selecting the most suitable audiphone for ahard-of-hearing person, comprising providing a group of microphoneinstruments having preselected different response characteristics in arelatively low frequency band and a group of amplifier instrumentshaving preselected different response characteristics in a relativelyhigh frequency band and a group of ear-phone instrument's havingpreselected different response characteristics in the interveningfrequency'band, establishing auditory communication between said personand any desired combination of three unlike instruments, and forming thecombinations by successively combining each of the instruments in onegroup with one instrument of each of the other two groups to find theinstrument having the most suitable response characteristics in thefrequency band of said one group and then repeating this procedure witheach other group to find'the instrument having the most suitableresponse characteristics in the frequency band of each of those groups.7

5. Apparatus for selecting and prescribing audiphones comprising a groupof microphones differing from each other in response characteristics ina predetermined low frequency portion of the frequency range transmittedby the audiphone, a group of ear-phones differing from each other inresponse characteristics in the next higher portion of said frequencyrange, a group of amplifiers differing from each other in responsecharacteristics in the high frequency portion of said frequency range, asource of cur-- rent supply, and means for selectively connecting eachof the instruments in each of said groups of instruments in circuitrelation with said source of current supply and with each of theinstruments in both of the other groups of instruments to find theinstrument having the most suitable response characteristics in each ofsaid portions of the frequency range.

6. Apparatus for selecting and prescribing audiphones comprising a groupof microphones differing in response characteristics up to frequenciesof substantially 800 cycles, a group of ear-phones differing from eachother in response characteristics in another portion of the frequencyrange transmitted by the audiphone, a group of amplifiers havingresponse characteristics differing from each other in the remainingportion of said frequency range, a source of current supply, and meansfor selectively connecting each of the instruments in each of saidgroups of instruments in circuit relation with said source of currentsupply and with each of the instruments in both of the other groups ofinstruments to find the instrument having the most suitable responsecharacteristics in each of said portions of 'the frequency range.

'7. Apparatus for selecting and prescribing audiphones comprising agroup of microphones differing from each other in responsecharacteristics in a predetermined low frequency portion of thefrequency range transmitted by the audiphone, a group of ear-phonesdiffering from each other in response characteristics in the next higherportion of said frequency range, a group of amplifiers having responsecharacteristics differing from each other above 1500 cycles; a source ofcurrent supply, and means for selectively connecting each of theinstruments in each of said groups of instruments in circuit relationwith said source of current supply and with each of the instruments inboth of the other groups of instruments to find the instrument havingthe most suitable response characteristics in each of said portions ofthe frequency range.

8. Apparatus for selecting and prescribing audiphones comprising a groupof. microphones difiering from each other in response characteristics ina predetermined portion of the frequency range transmitted by theaudiphone, a group of ear-phones differing from each other in responsecharacteristics in the. frequency band of from about 800 to 1500 cycles,a group of amplifiers differing from each other in responsecharacteristics in the remaining portionof said frequency range, asource of current supply, and means for selectively connecting each ofthe instruments in each of said groups of instruments in circuitrelation with said source of current supply and with each of theinstruments in both of the other groups of instruments to find theinstrument having the most suitable response characteristics in each ofsaid portions of the frequency range.

' SAMUEL F. LYBARGER.

